Fiber-optic based material property measurement system and related methods

ABSTRACT

An apparatus related method for measuring a property of a target material. The system may include a pump device that generates a pump beam. A modulation device may receive the pump beam and generate a modulated pump beam by modulating an intensity amplitude of the pump beam, which may be directed to the target material. A probe device may generate a probe beam, which is directed to the target material. A part of the probe beam may be reflected off of the target material, and has similar frequency characteristic as the modulated pump beam. A detection device may detect the reflected probe beam and produce a signal. An analyzing device may receive the signal and calculate the target material property by comparing the modulated frequency characteristics of the signal to those of the pump beam. At least one of the pump and the probe beams may be infrared light.

RELATED APPLICATIONS

The present application is a continuation application of U.S.application Ser. No. 16/311,413, filed Dec. 19, 2018, which is anational stage filing of International Application No.PCT/US2017/032390, filed on May 12, 2017, which claims priority under 35U.S.C § 119(e) from U.S. Provisional Application Ser. No. 62/353,263,filed Jun. 22, 2016, entitled “Fiber-Optic Based Material PropertyMeasurement System and Related Methods”; the disclosures of which areincorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to a fiber-optic based materialproperty measurement system and related methods.

BACKGROUND

One of the most sought after characterization tests in thermal propertytesting is the ability to test properties at elevated temperatures ineither simulated run-time environments or in situ during real timeoperation of parts. Examples of these types of measurements include theperiodic characterization of thermal barrier coatings (TBC) orenvironmental barrier coatings (EBC) on aircraft engine components, suchas turbine blades, over their lifetime, testing of microelectroniccomponents both during the fabrication process as well as in operationand in situ characterization of material degradation due to radiationdamage in reactor components.

In addition, silicon on sapphire (SOS) based material composites haveemerged as revolutionary solutions to a wide array of problems centeredaround silicon-on-insulator (SOI) devices and technologies. The commonlyused SOI platform is not used only because of raw performance, but alsodue to its ability to access the benefits of standard complementarymetal-oxide-semiconductor (CMOS) processing; more specifically, CMOSprocessing offers high manufacturing yields, low power operation andhigh levels of integration. In fact, issues that plague traditionallyengineered devices relying on the use of silicon handles, such asparasitic drain capacitance, electrical isolation, electromagnetic pulseinsulation, and cyclic durability and hysteresis, could in principle begreatly reduced or eliminated if a more robust material could be used asthe handle/substrate during CMOS processing.

These above mentioned issues that have plagued silicon (and GaAs)substrate use in CMOS have been virtually eliminated with thedemonstration of epitaxial grown silicon on a substrate of sapphire(Al₂O₃), creating the SOS process [1]. Silicon grown onto the surface ofsapphire is incredibly stable and offers virtually no hysteresis.Furthermore, in addition to being optically transparent in the visibleand near IR, Al₂O₃ is a much better electrical insulator than silicon orGaAs (the resistivity of Al₂O₃ can be in excess of 10¹⁶ Ω-cm, providingas good of insulation as SiO₂), which yields superior electricalisolation and drastic reduction in parasitic losses. The stability ofAl₂O₃ to high temperatures, aggressive chemistries, and high-energyradiation greatly out performs that of SiO₂, not to mention the thermalconductivity of Al₂O₃ is 20 times higher than that of fused silica [2,3]. This has positioned SOS-based technologies to provide cutting edgesolutions for RF applications, as several of the above-mentionedadvantages of SOS have resulted in operation of RF components anddevices (such as switches, mixers, etc.) operating to higher frequenciesand lower power [2, 4]. However, even beyond these specific RFapplications, SOS technology has allowed the realization of superiorperformance in analog-to-digital converters [5], monolithic digitalisolation buffers [6], energy harvesting devices [7], charge pumps [8],and temperature sensors [9].

Clearly, SOS technologies offer immense potential in a wide array oftechnologies. Critical in all of these technologies is the accurateknowledge of the thickness of the film composite layers that are gown onthe sapphire substrate, as this thickness dictates all static anddynamic performance metrics of the device layers. However, there iscurrently no non-destructive, non-contact metrology tool that canaccurately measure the thickness of thin films grown on sapphire wafers,which has limited the SOS process by potentially lowering yields.

Traditionally implemented “non-destructive” techniques for accuratedetermination of film thickness have mainly been optical-based. Forexample, ellipsometry has proven useful for measuring the thickness ofthin films on substrates, but the added difficulty of sapphire beingtransparent over a wide wavelength range can make ellipsometry difficultif the film on sapphire is too thin. Furthermore, the assumptions of thevarious optical properties of films that are necessary to analyzeellipsometry data can lead to large errors when the films are either toothin, unknown, or if multiple interfaces are in the measurement volume[10]. Additionally, and most notably for large scale processingapplications, ellipsometry measurements can be time consuming and notamenable for inserting into production lines or existing processingprocedures.

Other existing non-contact methods suffer the same fate as ellipsometrywhen attempting to provide a robust solution for film thicknessmeasurements of SOS samples. For example, direct absorption methods (inwhich reflectivity is monitored) have been used to characterize thethickness of thin films, but suffer large errors when the media ofinterest are only weakly absorbing and the volumetric absorptiondecreases as thickness decreases, making thin films very difficult tocharacterize; this therefore requires long “integration times” of theelectronics that severely limit the throughput of this characterizationtechnique [13]. Furthermore, these techniques have primarily beenoperated in visible range (or near UV and near IR) where many films ofinterest and, for that matter, the sapphire substrates, are nearlycompletely transmissive.

Short-pulsed-based acoustic wave techniques (such as picosecondacoustics) [14-16] that also rely on measuring reflectivity and relatingchanges in the time-resolved reflectivity to acoustic wave propagationsuffer from similar fates due to their requirements of localizedabsorption. While these techniques have proven robust to measure filmswith very small thicknesses (as thin as native oxide layers, ˜2 nm) [17,18], these techniques rely on spatially localized absorption, whichproves nearly impossible for transmissive systems unless a metal film iscoated on top. Furthermore, the use of a mechanical delay stage in this,or any transient reflectivity experiment utilizing short pulses, makesthese techniques inherently limited by the movement of the stage; thisis detrimental for integration into existing processes along withachieving the high throughput measurements required in this program.

Recent progress in pump-probe thermoreflectivity measurements [19, 20]has demonstrated promise in measuring the thickness of very thin films.Experiments based on thermoreflectivity rely on the principle ofthermoreflectance [21-23], i.e., the relatively small change inreflectivity that occurs due to temperature perturbations(thermoreflectance coefficients are typically on the order of 10⁻⁵-10⁻⁴l/K) [24-27]. Traditionally employed pump-probe thermoreflectancemeasurements have relied on short-pulsed systems and time varying therelative delay between the pump and probe [28, 29]. In this case, thepicosecond time resolution makes the time decay of the thermoreflectancesignal sensitive to small changes in thermal conductance that wouldarise from small changes in film thickness [30]. However, this approachrelies on short-pulsed laser systems with relatively large footprintsand mechanical delay stages, which, as mentioned previously, isdetrimental for rapid determination of film thickness and “retrofitting”into established processes.

However, a close cousin to time domain thermoflectance monitors thethermoreflectivity response of a sample in the frequency domain [31].This frequency domain thermoflectance (FDTR) method solely relies on afrequency dependent pump source that produces a modulated temperaturerise on the sample on frequency f [32]. Therefore, continuous wave (cw)lasers can be used as the pump and probe beams, and the pump modulationeven can be driven by digital modulation of the amplitude of theintensity of the pump beam at frequency f [33]. This alleviates the needfor mechanical delays, both speeding up measurements of thethermoreflectance signal along with ensuring smaller, more stable lasersystems (i.e., easier retrofitting into existing set ups). A FDTRmeasurement then consists of measuring the thermoreflectance signal(detected from lock in amplification) as a function of pump modulationfrequency. Due to the high frequency of modulation that can be achievedin an FDTR experiment, the measured signal is sensitive to small changesin thermal mass that arise due to film thickness. In fact, previousworks have used FDTR to measure the thickness of thin films on insultingsubstrates [34]. Furthermore, this experiment of CW modulated FDTR hasbeen shown to be able to accurately measure thicknesses of thin filmstacks including layers with encased single- and few-layer-graphene[33], which clearly demonstrates the promise of using FDTR to determinefilm thicknesses of thin films.

A schematic of an embodiment of an FDTR experiment 301 for measuringproperties of a target material 321 is shown in FIG. 3 . A cw laserproduces a laser beam 310 which is separated into a pump beam 316 andprobe beam 312 by optical device 323. The pump beam 316 is directed to amodulator 313 via optical component 331. The amplitude of the intensityof the pump beam 316 is modulated by modulator 313 to produce amodulated pump beam 314. The modulated pump beam 314 and probe beam 312are directed to a focusing device 325 by optical components 333, 334,332, 335, 324, 327 (for example, mirror or semi-reflective mirror). Thefocusing device 325 directs the modulated pump beam 314 and the probebeam to the target material 321. The probe beam 312 at least partiallyreflects from the target material 321, and is received by detector 329.The modulated pump beam 314 is at least partially absorbed by the targetmaterial 321, which results in local heating. The heating causes achange in the reflectance of the target material 321. As a result of thechange in reflectance, the optical properties of a reflected probe beam328 change, which is directed to the detector 329. To produce a FDTRmeasurement, the modulator changes the frequency of the modulation ofthe intensity of the modulated pump beam 314, which produces a reflectedprobe beam 328 having similar frequency characteristics. By comparingthe frequency characteristics of the modulated pump beam 314 with thefrequency characteristics of the reflected probe beam 328 with analyzingdevice 319, a measurement of the properties of target material 321, suchas a thickness, can be made.

The issue with FDTR in its traditionally employed configuration formeasuring SOS materials and multilayers in situ lies in the same realmas the other aforementioned reflectivity/absorptivity experiments:namely, FDTR is reliant on near-surface absorption and subsequentreflection of both pump and probe beams to ensure the enhancedsensitivity to small changes in thermal mass, and subsequently filmthicknesses. In its traditional implementation, FDTR experiments requirethe deposition of a thin metal film transducer on top of the sample ofinterest, which serves to ensure absorption of the pump and probe withinthe optical skin depth of the metal (near surface). Clearly, this metalfilm transducer requirement will render traditionally used FDTR lasersources (i.e., wavelengths) and implementation unacceptable for in situand non-contact characterization of thin films in SOS multilayer stacks.

In addition, existing FDTR methods require measurement devices thatutilize free-space optics.

An example of an embodiment of an FDTR is shown in FIG. 3 . Such anembodiment of the device require precise alignment and tuning, andrequire large components. The degree of complexity and large footprintprecludes their use, for example, in situ.

An aspect of an embodiment of the present invention approach presents amajor advancement in FDTR technology that will provide the opportunityfor application for SOS, and for in situ measurements.

Overview

An aspect of an embodiment of the present invention solves the problemof, among other things, measuring properties, such as thickness, oftarget materials, such sapphire or SOS devices. An embodiment of theinvention may also be made smaller such that it may be portable, or usedin situ. Furthermore, an embodiment of the invention may achievemodulation speeds that are faster than typical FDTR devices, which allowfor faster measurement of properties, such as thickness. Additionally,an embodiment of the invention may provide increased sensitivity tosurface properties or the properties of very thin layers due to theincreased modulation frequencies. An aspect of an embodiment of thepresent invention provides, but not limited thereto, a method formeasuring at least one property of a target material usingthermoreflectance. The method may comprise: generating a pump light beamat a pump wavelength with a pump device; generating a modulated pumpbeam by modulating an amplitude of an intensity of the pump light beambetween at least a first modulation frequency and a second modulationfrequency; directing at least a portion of the modulated pump beam to amanipulation portion of the target material; generating a probe beam ata probe wavelength with a probe device; and directing at least a portionof the probe beam to a probing portion of the target material, whereinat least a part of the portion of the probe beam is reflected off of thetarget material forming a reflected probe beam, wherein the reflectedprobe beam has a similar modulated frequency characteristic as the pumpbeam. The method may further comprise: directing at least a portion ofthe reflected probe beam to a detection device, wherein the detectiondevices generates a detection signal from the reflected probe beam;analyzing the detection signal with an analyzing device by receiving thedetection signal with the analyzing device, and calculating the propertyof the target material by comparing the modulated frequencycharacteristics of the reflected probe beam to the modulated frequencycharacteristics of the pump beam; and wherein at least one of the pumpwavelength and the probe wavelength is an infrared wavelength.

An aspect of an embodiment of the present invention provides, but notlimited thereto, an apparatus for measuring at least one property of atarget material using thermoreflectance. The apparatus may comprise: apump device that generates a pump light beam at a pump wavelength; afirst direction apparatus that directs the pump light beam to amodulation device, wherein the modulation device generates a modulatedpump beam by modulating an amplitude of an intensity of the pump lightbeam between at least a first modulation frequency and a secondmodulation frequency; a second direction apparatus that directs at leasta portion of the modulated pump beam to a manipulation portion of thetarget material; a probe device that generates a probe beam at a probewavelength; a third direction apparatus that directs at least a portionof the probe beam to a probing portion of the target material, whereinat least a part of the portion of the probe beam is reflected off of thetarget material forming a reflected probe beam, wherein the reflectedprobe beam has a similar modulated frequency characteristic as the pumpbeam; a detection device that detects at least a portion of thereflected probe beam, and produces a detection signal from the reflectedprobe beam; an analyzing device receives the detection signal andcalculates the property of the target material by comparing themodulated frequency characteristics of the reflected probe beam to themodulated frequency characteristics of the pump beam; and wherein atleast one of the pump wavelength and the probe wavelength is an infraredwavelength.

An aspect of an embodiment of the present invention provides, but notlimited thereto, an apparatus for measuring at least one property of atarget material using thermoreflectance. The apparatus may comprise: apump device that generates a pump light beam at a pump wavelength; afirst direction apparatus that directs the pump light beam to amodulation device, wherein the modulation device generates a modulatedpump beam by modulating an amplitude of the an intensity of the pumplight beam between at least a first modulation frequency and a secondmodulation frequency, a second direction apparatus that directs at leasta portion of the modulated pump beam to a manipulation portion of thetarget material; a probe device that generates a probe beam at a probewavelength; a third direction apparatus that directs at least a portionof the probe beam to a probing portion of the target material, whereinat least a part of the portion of the probe beam is reflected off of thetarget material forming a reflected probe beam, wherein the reflectedprobe beam has a similar modulated frequency characteristic as the pumpbeam; a detection device that detects at least a portion of thereflected probe beam, and produces a detection signal from the reflectedprobe beam; an analyzing device receives the detection signal andcalculates the property of the target material by comparing themodulated frequency characteristics of the reflected probe beam to themodulated frequency characteristics of the pump beam; and wherein thepump device, the modulation device, the first direction apparatus, thesecond direction apparatus, the probe device, the third directionapparatus comprise fiber optic devices.

An aspect of an embodiment of the present invention provides, but notlimited thereto, an apparatus related method for measuring a property ofa target material. The system may include a pump device that generates apump beam. A modulation device may receive the pump beam and generate amodulated pump beam by modulating an intensity amplitude of the pumpbeam, which may be directed to the target material. A probe device maygenerate a probe beam, which is directed to the target material. A partof the probe beam may be reflected off of the target material, and hassimilar frequency characteristic as the modulated pump beam. A detectiondevice may detect the reflected probe beam and produce a signal. Ananalyzing device may receive the signal and calculate the targetmaterial property by comparing the modulated frequency characteristicsof the signal to those of the pump beam. At least one of the pump andthe probe beams may be infrared light.

These and other objects, along with advantages and features of variousaspects of embodiments of the invention disclosed herein, will be mademore apparent from the description, drawings and claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the presentinvention, as well as the invention itself, will be more fullyunderstood from the following description of preferred embodiments, whenread together with the accompanying drawings.

The accompanying drawings, which are incorporated into and form a partof the instant specification, illustrate several aspects and embodimentsof the present invention and, together with the description herein,serve to explain the principles of the invention. The drawings areprovided only for the purpose of illustrating select embodiments of theinvention and are not to be construed as limiting the invention.

FIG. 1 represents the reflectivity and absorption for sapphire.

FIG. 2 represents the reflectivity and absorption for SiO₂.

FIG. 3 schematically represents an example of an embodiment of an FDTRdevice.

FIG. 4 schematically represents a FDTR device of an embodiment of theinvention.

FIG. 5 schematically represents a FDTR device of an embodiment of theinvention.

FIG. 6 schematically represents a FDTR device of an embodiment of theinvention.

FIG. 7 represents an example of an FDTR data signal as a function ofpump modulation frequency.

FIG. 8 schematically represents a modulated pump beam and a probe beamdirected to a target material according to an embodiment of theinvention.

FIG. 9 schematically represents a modulated pump beam and a probe beamdirected to a target material according to an embodiment of theinvention.

FIG. 10 schematically represents a modulated pump beam and a probe beamdirected to a target material according to an embodiment of theinvention.

FIG. 11 schematically represents a modulated pump beam and a probe beamdirected to a target material according to an embodiment of theinvention.

FIG. 12 represents experimental results of an embodiment of theinvention using a monolayer and 300 nm of epi-silicon on sapphire.

FIG. 13 represents experimental results of an embodiment of theinvention using a thin oxide less than 50 nm and epi-silicon/sapphire.

FIG. 14 represents experimental results of an embodiment of theinvention using a monolayer and 300 nm of p-Si or a-Si/thinoxide/sapphire.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Although example embodiments of the present disclosure are explained indetail herein, it is to be understood that other embodiments arecontemplated. Accordingly, it is not intended that the presentdisclosure be limited in its scope to the details of construction andarrangement of components set forth in the following description orillustrated in the drawings. The present disclosure is capable of otherembodiments and of being practiced or carried out in various ways.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Ranges may beexpressed herein as from “about” or “approximately” one particular valueand/or to “about” or “approximately” another particular value. When sucha range is expressed, other exemplary embodiments include from the oneparticular value and/or to the other particular value.

The term “about,” as used herein, means approximately, in the region of,roughly, or around. When the term “about” is used in conjunction with anumerical range, it modifies that range by extending the boundariesabove and below the numerical values set forth. In general, the term“about” is used herein to modify a numerical value above and below thestated value by a variance of 10%. In one aspect, the term “about” meansplus or minus 10% of the numerical value of the number with which it isbeing used. Therefore, about 50% means in the range of 45%-55%.Numerical ranges recited herein by endpoints include all numbers andfractions subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.90, 4, 4.24, and 5). Similarly, numerical ranges recitedherein by endpoints include subranges subsumed within that range (e.g. 1to 5 includes 1-1.5, 1.5-2, 2-2.75, 2.75-3, 3-3.90, 3.90-4, 4-4.24,4.24-5, 2-5, 3-5, 1-4, and 2-4). It is also to be understood that allnumbers and fractions thereof are presumed to be modified by the term“about.”

By “comprising” or “containing” or “including” is meant that at leastthe named compound, element, particle, or method step is present in thecomposition or article or method, but does not exclude the presence ofother compounds, materials, particles, method steps, even if the othersuch compounds, material, particles, method steps have the same functionas what is named.

In describing example embodiments, terminology will be resorted to forthe sake of clarity. It is intended that each term contemplates itsbroadest meaning as understood by those skilled in the art and includesall technical equivalents that operate in a similar manner to accomplisha similar purpose. It is also to be understood that the mention of oneor more steps of a method does not preclude the presence of additionalmethod steps or intervening method steps between those steps expresslyidentified. Steps of a method may be performed in a different order thanthose described herein without departing from the scope of the presentdisclosure. Similarly, it is also to be understood that the mention ofone or more components in a device or system does not preclude thepresence of additional components or intervening components betweenthose components expressly identified.

Some references, which may include various patents, patent applications,and publications, are cited in a reference list and discussed in thedisclosure provided herein. The citation and/or discussion of suchreferences is provided merely to clarify the description of the presentdisclosure and is not an admission that any such reference is “priorart” to any aspects of the present disclosure described herein. In termsof notation, “[n]” corresponds to the n^(th) reference in the list. Allreferences cited and discussed in this specification are incorporatedherein by reference in their entireties and to the same extent as ifeach reference was individually incorporated by reference.

A detailed description of aspects of the present disclosure will now beprovided with reference to the accompanying drawings. The drawings forma part hereof and show, by way of illustration, specific embodiments orexamples. In referring to the drawings, like numerals represent likeelements throughout the several figures.

FIG. 4 schematically illustrates an exemplary embodiment of afrequency-domain thermoreflectance (FDTR) device 401 for measuringproperties, such as thickness, of a target material 421.

A pump beam source 415 generates a pump beam 416, which is directed tomodulator 413 via pump beam direction apparatus 443. The amplitude ofthe intensity of the pump beam 416 is modulated by modulator 413 toproduce a modulated pump beam 414. The modulated pump beam 414 isdirected to the target material 421 via a modulated pump beam directionapparatus 444. The modulated pump beam direction apparatus may includecombining device 409 and focusing device 425 (for example, a microscopeobjective). The probe beam 412 and modulated pump beam 414 may becombined by combining device 409 into combined beam 441.

A probe beam source 411 generates a probe beam 412, which is directed tothe source via a probe beam direction apparatus 442. The probe beamdirection apparatus may include combining device 409 and focusing device425 (e.g., focusing device).

The probe beam 412 at least partially reflects from the target material421, creating a reflected probe beam 428. The reflected probe beam 428is received by detector 429 via a reflected probe beam directionapparatus 448. The reflected probe beam direction apparatus 448 mayinclude focusing device 425. The reflected probe beam directionapparatus 448 may include an optical isolator 405 to isolate thereflected probe beam 428 from other signals.

The modulated pump beam 414 is at least partially absorbed by the targetmaterial 421, which results in surface heating. The heating causes achange in the reflectance of the target material 421. As a result of thechange in reflectance due to temperature change, the optical propertiesof a reflected probe beam 428 change, which is detected by the detector429. To produce a FDTR measurement, the modulator changes the frequencyof the modulation of the intensity of the modulated pump beam 414, forexample by sweeping between a first and a second modulation frequency,which produces a reflected probe beam 428 having similar frequencycharacteristics. By comparing the frequency characteristics of themodulated pump beam 414 with the frequency characteristics of thereflected probe beam 428 detected by detector 429, a measurement of theproperties of target material 421, such as a thickness, can be made.

It should be appreciated that the target material 421 may includesapphire, such as SOS. As discussed above, typical FDTR device areoperated in visible range (or near UV and near IR) where films ofinterest, such as a sapphire substrates, are nearly completelytransmissive. FIGS. 1 and 2 show the reflectivity and absorption forsapphire and SiO₂, respectively. Sapphire experiences coupling betweeninfrared (IR) photons and optical phonons, known as phonon-polaritons.Excitation of these phonon-polaritons can be achieved through direct IRirradiation of, for example, oxide films, nitride films and sapphiresubstrates. The result is that sapphire becomes absorptive toirradiating light, which is necessary to create heating and thusreflectivity changes for FDTR. In addition, the temperature rise of thesapphire from the phonon-polariton absorption mechanism relaxes nearlyinstantly, for example, in less than a nanosecond, which allows forquicker modulation, and faster measurement of properties such asthickness.

Therefore, it shall be appreciated that invention may use light that isat least partially absorptive to sapphire, such as IR light, as the pumpbeam. In one embodiment, the pump beam wavelength may be in the rangeabout 200 nm to about 15 μm. The pump beam wavelength may further be inthe range of about 5 μm to about 15 μm. The pump beam wavelength mayfurther be in the range of about 7 μm to about 13 μm. The pump beamwavelength may further be in the range of about 8 μm to about 12 μm. Thepump beam wavelength may further be in the range of about 10 μm to about12 μm. The pump beam wavelength may further be about 1550 nm. The pumpbeam wavelength may further be in the range of about 720 nm to about 890nm. The pump beam wavelength may further be about 980 nm. The probe beammay be light that is at least partially reflective to, for example,sapphire. The probe beam wavelength may be in the range of about 200 nmto about 15 μm. The probe beam wavelength may be in the range of about10 μm to about 15 μm. The probe beam wavelength may further be in therange of about 11 μm to about 15 μm. The probe beam wavelength mayfurther be in the range of about 10 μm to about 13 μm. The probe beamwavelength may further be in the range of about 11 μm to about 13 μm.The probe beam wavelength may further be in the range of about 10 μm toabout 12 μm. The probe beam wavelength may further be in the range ofabout 11 μm to about 12 μm. The probe beam wavelength may further be inthe range of about 720 nm to about 890 nm. The probe beam wavelength mayfurther be 980 nm. The probe beam wavelength may further be about 1550nm. In one embodiment of the invention, the pump beam wavelength may bedifferent from the probe beam wavelength. In a further embodiment of theinvention, the pump beam wavelength may be larger than the probe beamwavelength. In a further embodiment of the invention, the pump beamwavelength may be smaller than the probe beam wavelength. In oneembodiment of the invention, the pump beam wavelength may be the same asthe probe beam wavelength. The modulation frequencies may be in therange of about 10 Hz to about 100 GHz. The modulation frequencies mayfurther be in the range of about 10 Hz to about 40 GHz. The modulationfrequencies may further be in the range of about 10 Hz to about 5 GHz.The modulation frequencies may further be in the range of about 0 Hz toabout 1 GHz. The modulation frequencies may further be in the range ofabout 1 GHz to about 100 GHz. The modulation frequencies may further bein the range of about 1 GHz to about 40 GHz. The modulation frequenciesmay further be in the range of about 1 GHz to about 5 GHz. Themodulation frequencies may be in the range of about 5 GHz to about 100GHz. Still yet, the modulation frequencies may be in the range of about5 GHz to about 40 GHz. The spot size may be in the range from 1 μm to 50μm (the spot size may be less than 1 μm or greater than 50 μm).

It shall also be appreciated that FDTR device 401 may utilize free spaceoptical components. It may also utilize fiber optic components. Forexample, the pump beam direction apparatus 443, the modulated pump beamdirection apparatus 444, the probe beam direction apparatus 442, and thereflected probe beam direction apparatus 448 may include fiber opticdevices. The pump beam source 415 and the probe beam source 411 may befiber lasers, such as fiber coupled lasers or in-fiber lasers. The pumpbeam source 415 and the probe beam source 411 may be single mode fiberlasers, or multimode fiber lasers. The modulator 413 may be an in-fibermodulation device. The combining device 409 and focusing device 425 mayalso be fiber optic devices. The focusing device may be a fiber coupledobjective lens. The optical isolator 405 may be a fiber optic isolator.By using fiber optic devices, the FDTR device 401 may be made smallerthan traditional FDTR devices. It may be sufficiently small and durablesuch to be used in situ.

FIG. 5 schematically illustrates another exemplary embodiment of a FDTRdevice 501 for measuring properties, such as thickness, of a targetmaterial 521.

A pump beam source 515 generates a pump beam 516, which is directed tomodulator 513 via pump beam direction apparatus 543. The amplitude ofthe intensity of the pump beam 516 is modulated by modulator 513 toproduce a modulated pump beam 514. The modulated pump beam 514 isdirected to the target material 521 via a modulated pump beam directionapparatus 544. The modulated pump beam direction apparatus may includecombining device 575 and focusing device 525. The combining device 575may be a wavelength division multimeter (WMD).

A probe beam source 511 generates a probe beam 512, which is directed tothe source via a probe beam direction apparatus 542. The probe beamdirection apparatus may include combining device 575 and focusing device525. The probe beam direction apparatus may also include opticalisolator 571, which outputs probe beam 593. The probe beam directionapparatus may include optical circulator 573, which outputs probe beam594.

The probe beam 512 at least partially reflects from the target material521, creating a reflected probe beam 528. The reflected probe beam 528received by detector 529 via a reflected probe beam direction apparatus548. The reflected probe beam direction apparatus 548 may includecombining device 575, which outputs reflected probe beam 595, andfocusing device 525. The reflected probe beam direction apparatus 548may include an optical isolator 505 to isolate the reflected probe beam528 from other signals. The reflected probe beam direction apparatus 548may also include optical circulator 573. The probe beam 512 andmodulated pump beam 514 may be combined by combining device 575 intocombined beam 591.

The modulated pump beam 514 is at least partially absorbed by the targetmaterial 521, which results in surface heating. The heating causes achange in the reflectance of the target material 521. As a result of thechange in reflectance due to temperature change, the optical propertiesof a reflected probe beam 528 change, which is detected by the detector529. To produce a FDTR measurement, the modulator changes the frequencyof the modulation of the intensity of the modulated pump beam 514, forexample by sweeping between a first and a second modulation frequency,which produces a reflected probe beam 528 having similar frequencycharacteristics. By comparing the frequency characteristics of themodulated pump beam 514 with the frequency characteristics of thereflected probe beam 528 detected by detector 529, a measurement of theproperties of target material 521, such as a thickness, can be made.

Optical components 502 of the FDTR device 501 may be controlled byelectrical components 560. The pump source 515 may be controlled bylaser diode drive 562 and thermoelectric control module 563. The probesource 515 may be controlled by laser diode drive 564 and thermoelectriccontrol module 565. The modulator 513 may be controlled by vectornetwork analyzer (VNA) 520. A modulation signal may be amplified bypower amplifier 567, for example, an RF power amplifier, which producesa drive signal 569, for example, an RF drive signal. The detector 529may be a photodiode, for example an InGaAs photodiode. The detector 529supplies a detection signal from the reflected probe beam 528 to the VNA520. The detection signal may be supplied via an amplifier 568, forexample, a low noise RF amplifier. The VNA 520 performs the comparisonbetween the properties of the modulated pump beam and the reflectedprobe beam.

It should be appreciated that the target material 521 may includesapphire, such as SOS. Therefore, it shall be appreciated that inventionmay use light that is at least partially absorptive to sapphire, such asIR light, as the pump beam. In one embodiment, the pump beam wavelengthmay be in the range about 200 nm to about 15 μm. The pump beamwavelength may further be in the range of about 5 μm to about 15 μm. Thepump beam wavelength may further be in the range of about 7 μm to about13 μm. The pump beam wavelength may further be in the range of 8 μm to12 μm. The pump beam wavelength may further be in the range of about 10μm to about 12 μm. The pump beam wavelength may further be about 1550nm. The pump beam wavelength may further be in the range of about 720 nmto about 890 nm. The pump beam wavelength may further be about 980 nm.The probe beam may be light that is at least partially reflective to,for example, sapphire. The probe beam wavelength may be in the range ofabout 200 nm to about 15 μm. The probe beam wavelength may be in therange of about 10 μm to about 15 μm. The probe beam wavelength mayfurther be in the range of about 11 μm to about 15 μm. The probe beamwavelength may further be in the range of about 10 μm to about 13 μm.The probe beam wavelength may further be in the range of about 11 μm toabout 13 μm. The probe beam wavelength may further be in the range ofabout 10 μm to about 12 μm. The probe beam wavelength may further be inthe range of about 11 μm to about 12 μm. The probe beam wavelength mayfurther be in the range of about 720 nm to about 890 nm. The probe beamwavelength may further be about 980 nm. The probe beam wavelength mayfurther be about 1550 nm. In one embodiment of the invention, the pumpbeam wavelength may be different from the probe beam wavelength. In afurther embodiment of the invention, the pump beam wavelength may belarger than the probe beam wavelength. In a further embodiment of theinvention, the pump beam wavelength may be smaller than the probe beamwavelength. In one embodiment of the invention, the pump beam wavelengthmay be the same as the probe beam wavelength. The modulation frequenciesmay be in the range of about 10 Hz to about 100 GHz. The modulationfrequencies may further be in the range of about 10 Hz to about 40 GHz.The modulation frequencies may further be in the range of about 10 Hz toabout 5 GHz. The modulation frequencies may further be in the range ofabout 10 Hz to about 1 GHz. The modulation frequencies may further be inthe range of about 1 GHz to about 100 GHz. The modulation frequenciesmay further be in the range of about 1 GHz to about 40 GHz. Themodulation frequencies may further be in the range of about 1 GHz toabout 5 GHz. The modulation frequencies may be in the range of 5 aboutGHz to about 100 GHz. Still yet, the modulation frequencies may be inthe range of about 5 GHz to about 40 GHz. The spot size may be in therange from 1 μm to about 50 μm (the spot size may be less than 1 μm orgreater than 50 μm).

It shall also be appreciated that FDTR device 501 may utilize free spaceoptical components. It may also utilize fiber optic components. Forexample, the pump beam direction apparatus 543, the modulated pump beamdirection apparatus 544, the probe beam direction apparatus 542, and thereflected probe beam direction apparatus 548 may include fiber opticdevices. The pump beam source 515 and the probe beam source 511 may befiber lasers, such as fiber coupled lasers or in-fiber lasers. The pumpbeam source 515 and the probe beam source 511 may be single mode fiberlasers, or multimode fiber lasers. The modulator 513 may be an in-fibermodulation device. The combining device 575 and focusing device 525 mayalso be fiber optic devices. The focusing device 525 may be a fibercoupled objective lens. The optical isolator 505 may be a fiber opticisolator. The optical isolator 571 may be a fiber optic isolator. Theoptical circulator 573 may be a fiber optic circulator. By using fiberoptic devices, the FDTR device 501 may be made smaller than traditionalFDTR devices. It may be sufficiently small and durable such to be usedin situ.

FIG. 6 schematically illustrates another exemplary embodiment of a FDTRdevice 601 for measuring properties, such as thickness, of a targetmaterial 621. Unlike FDTR devices 401 and 501, FDTR device 601 does notuse a same beam path for the modulated pump beam and the probe beam.

A pump beam source 615 generates a pump beam 616, which is directed tomodulator 613 via pump beam direction apparatus 643. The amplitude ofthe intensity of the pump beam 616 is modulated by modulator 613 toproduce a modulated pump beam 614. The modulated pump beam 614 isdirected to the target material 621 via a modulated pump beam directionapparatus 644. The modulated pump beam direction apparatus may include amodulated pump beam focusing device.

A probe beam source 611 generates a probe beam 612, which is directed tothe source via a probe beam direction apparatus 642. The probe beamdirection apparatus may include a probe beam focusing device.

The probe beam 612 at least partially reflects from the target material621, creating a reflected probe beam 628. The reflected probe beam 628received by detector 629 via a reflected probe beam direction apparatus648. The reflected probe beam direction apparatus 648 may include afocusing device. The reflected probe beam direction apparatus 648 mayinclude an optical isolator to isolate the reflected probe beam 628 fromother signals.

The modulated pump beam 614 is at least partially absorbed by the targetmaterial 621, which results in surface heating. The heating causes achange in the reflectance of the target material 621. As a result of thechange in reflectance due to temperature change, the optical propertiesof a reflected probe beam 628 change, which is detected by the detector629. To produce a FDTR measurement, the modulator changes the frequencyof the modulation of the intensity of the modulated pump beam 614, forexample by sweeping between a first and a second modulation frequency,which produces a reflected probe beam 628 having similar frequencycharacteristics. By comparing the frequency characteristics of themodulated pump beam 614 with the frequency characteristics of thereflected probe beam 628 detected by detector 629, a measurement of theproperties of target material 621, such as a thickness, can be made.

It should be appreciated that the target material 621 may includesapphire, such as SOS. Therefore, it shall be appreciated that inventionmay use light that is at least partially absorptive to sapphire, such asIR light, as the pump beam. In one embodiment, the pump beam wavelengthmay be in the range about 200 nm to 15 μm. The pump beam wavelength mayfurther be in the range of 5 μm to 15 μm. The pump beam wavelength mayfurther be in the range of 7 μm to 13 μm. The pump beam wavelength mayfurther be in the range of 8 μm to 12 μm. The pump beam wavelength mayfurther be in the range of 10 μm to 12 μm. The pump beam wavelength mayfurther be 1550 nm. The pump beam wavelength may further be in the rangeof 720 nm to 890 nm. The pump beam wavelength may further be 980 nm. Theprobe beam may be light that is at least partially reflective to, forexample, sapphire. The probe beam wavelength may be in the range ofabout 200 nm to about 15 μm. The probe beam wavelength may be in therange of about 10 μm to about 15 μm. The probe beam wavelength mayfurther be in the range of about 11 μm to about 15 μm. The probe beamwavelength may further be in the range of about 10 μm to about 13 μm.The probe beam wavelength may further be in the range of about 11 μm toabout 13 μm. The probe beam wavelength may further be in the range ofabout 10 μm to about 12 μm. The probe beam wavelength may further be inthe range of about 11 μm to about 12 μm. The probe beam wavelength mayfurther be in the range of about 720 nm to about 890 nm. The probe beamwavelength may further be about 980 nm. The probe beam wavelength mayfurther be about 1550 nm. In one embodiment of the invention, the pumpbeam wavelength may be different from the probe beam wavelength. In afurther embodiment of the invention, the pump beam wavelength may belarger than the probe beam wavelength. In a further embodiment of theinvention, the pump beam wavelength may be smaller than the probe beamwavelength. In one embodiment of the invention, the pump beam wavelengthmay be the same as the probe beam wavelength. The modulation frequenciesmay be in the range of about 10 Hz to about 100 GHz. The modulationfrequencies may further be in the range of about 10 Hz to about 40 GHz.The modulation frequencies may further be in the range of about 10 Hz toabout 5 GHz. The modulation frequencies may further be in the range ofabout 10 Hz to about 1 GHz. The modulation frequencies may further be inthe range of about 1 GHz to about 100 GHz. The modulation frequenciesmay further be in the range of about 1 GHz to about 40 GHz. Themodulation frequencies may further be in the range of about 1 GHz toabout 5 GHz. The modulation frequencies may be in the range of about 5GHz to about 100 GHz. Still yet, the modulation frequencies may be inthe range of about 5 GHz to about 40 GHz. The spot size may be in therange from about 1 μm to about 50 μm (the spot size may be less than 1μm or greater than 50 μm).

It shall also be appreciated that FDTR device 601 may utilize free spaceoptical components. It may also utilize fiber optic components. Forexample, the pump beam direction apparatus 643, the modulated pump beamdirection apparatus 644, the probe beam direction apparatus 642, and thereflected probe beam direction apparatus 648 may include fiber opticdevices. The pump beam source 615 and the probe beam source 611 may befiber lasers, such as fiber coupled lasers or in-fiber lasers. The pumpbeam source 615 and the probe beam source 611 may be single mode fiberlasers, or multimode fiber lasers. The modulator 613 may be an in-fibermodulation device. The combining device focusing device may also befiber optic devices. The modulated pump beam focusing device and theprobe beam focusing device may be a fiber coupled objective lens. Theoptical isolator may be a fiber optic isolator. By using fiber opticdevices, the FDTR device 601 may be made smaller than traditional FDTRdevices. It may be sufficiently small and durable such to be used insitu.

FIGS. 8-11 schematically illustrates an example of target material beingtested with an embodiment of an FDTR device. A FDTR device 801 generatesmodulated pump beam 815, and probe beam 811. FIG. 8 shows targetmaterial 841, FIG. 9 shows target material 843, FIG. 10 shows targetmaterial 845, and FIG. 11 shows target material 843. Target material 841may, for example be sapphire. Target material or layer 845 may be forexample, an oxide layer. Target material or layer 843 may be, forexample, a silicon layer.

FIG. 8 shows the modulated pump beam 815 is at least partially absorbedin the target material 841, and the probe beam 811 is at least partiallyreflected by the target material 841. The target material 841 is, forexample, sapphire. The at least partial absorption of modulated pumpbeam 815 causes localized heating 861 of the target material 841. Theshading of the modulated pump beam 815 shows that at least part of thepump beam is being absorbed as it travels through the target material841. Therefore, a measurement of a property of the target material 841,for example a thickness, may be performed.

FIG. 9 shows the modulated pump beam 815 is at least partially absorbedin the layer 841, and the probe beam 811 is at least partially reflectedby the layer 841. The layer 841 is, for example, sapphire. The at leastpartial absorption of modulated pump beam 815 causes localized heating861 of the layer 841. The shading of the modulated pump beam 815 showsthat at least part of the pump beam is being absorbed as it travelsthrough the layer 841. Both the modulated pump beam 815 and the probebeam 811 are transparent to target material 843, for example, a siliconlayer. The presence of target material 843, the effects of which aredescribed further below, changes the characteristics of the reflectedprobe beam 811. Therefore, a measurement of a property of targetmaterial 843, for example a thickness, may be performed.

FIG. 10 shows the modulated pump beam 815 is at least partially absorbedin the target material 845, and the probe beam 811 is at least partiallyreflected by the target material 845. The target material 845 is, forexample, an oxide layer. The at least partial absorption of modulatedpump beam 815 causes localized heating 861 of the target material 845.The shading of the modulated pump beam 815 shows that at least part ofthe pump beam is being absorbed as it travels through the targetmaterial 845. Therefore, a measurement of a property of the targetmaterial 845, for example a thickness, may be performed.

FIG. 11 shows the modulated pump beam 815 is at least partially absorbedin layer 845, for example, an oxide layer, and the probe beam 811 is atleast partially reflected by layer 845. The at least partial absorptionof modulated pump beam 815 causes localized heating 861 of the layer845. The shading of the modulated pump beam 815 shows that at least partof the pump beam is being absorbed as it travels through the layer 845.Both the modulated pump beam 815 and the probe beam 811 are transparentto target layer 843, for example, a silicon layer. The presence oftarget layer 843, the effects of which are described further below,changes the characteristics of the reflected probe beam 811. Therefore,a measurement of a property of target layer 843, for example athickness, may be performed.

It should be appreciated that the configurations of FIGS. 9 and 11 takeadvantage of layer 843, for example, silicon, being transparent to IRlight. The polaritons are excited on the surface of the target material841, for example, sapphire, causing a modulated thermal event that isdetected by the probe beam. Subsequently, the heat decays into both thetarget material 841 as well as layer 843. In the case where there is nofilm on top of the target material as shown in FIG. 8 , the thermalsignature will be distinctly different because of the lack of thermalmass transferring some of the heat away from target material.

The aforementioned embodiments demonstrate improved FDTR device. Theinvention may thus be used to measure properties, such as thickness, oftarget materials, such sapphire or SOS devices. The invention may alsobe made smaller such that it may be portable, or used in situ.Furthermore, it may achieve modulation speeds that are faster thantypical FDTR devices, which allow for faster measurement of properties,such as thickness. Additionally, it may provide increased sensitivity tosurface properties or the properties of very thin layers due to theincreased modulation frequencies.

EXAMPLES

Practice of an aspect of embodiments of the invention will be still morefully understood from the following examples and simulated results,which are presented herein for illustration only, and should not beconstrued as limiting the invention in any way.

Reflectivity measurements from, for example, the embodiments of FIGS.4-6 , at wavelengths that adequately heat a sample and subsequentlyprobe a frequency dependent reflectivity response, may be used tomeasure a thickness of various films on sapphire. For example, infraredwavelengths may be utilized. In an embodiment of the invention, infraredFDTR can take advantage of coupling between infrared photons and opticalphonons, the result of which is known as phonon-polaritons. In anembodiment of the invention, excitation of these phonon-polaritons maybe achieved through direct infrared irradiation of oxide films, nitridefilms, and a sapphire substrate. The subsequent temperature rise of, forexample, sapphire from the phonon-polariton absorption mechanism, whichmay relax nearly instantly, for example, sub nanosecond relaxation,compared to the time/frequency scale of measurement, for example, tennanoseconds or greater, may enable robust FDTR analysis to be applied,which may be ultrasensitive to small changes in film thickness. Usingthis knowledge, an embodiment of the invention may perform FDTR onvarious stacks of interest by choosing a pump wavelength that may excitephonon-polaritons, causing a heating event on the surface of a materialin question, and a probe wavelength that may reflect such that thechange in the probe thermoreflectivity response over a wide range ofpump modulation frequencies is observed. Examples of pump modulationfrequencies are included in FIG. 7 , which shows an example of an FDTRdata signal as a function of pump modulation frequency.

The ability to create a spatially localized heating event in oxide,nitride, and sapphire may allow an embodiment of the invention theflexibility to measure all of the film stacks discussed below. Theexamples below demonstrates rigorous simulations of an embodimentinvention, and specifically demonstrates the sensitivity of themeasurements made by an embodiment invention to film thicknesses. Thesesimulations below are based on solutions to the multilayer heat equationin the frequency domain and accounts for detection from, for example, alock in amplifier [29, 31, 32, 35]. In short, the examples discussedbelow are simulated experiments that represent the real sensitivity ofan embodiment of the invention to film thickness. Clearly, an embodimentof the invention may offer exceptional sensitivity to film thickness ofvarious visibly transparent films on sapphire substrates, as describedin the examples below. Thus, an embodiment of the invention redefinesthe current state of the art for non-contact, non-destructive filmthickness measurements of visible or transparent film stacks whileoffering nanometer resolution and rapid film thickness measurements onthe order of seconds.

Example and Experimental Results Set No. 1: Between a Monolayer and 300nm of Epi-Silicon on Sapphire

This embodiment of the invention takes advantage of silicon beingtransparent to infrared light. Polaritons may be excited on the surfaceof, for example, sapphire, causing a modulated thermal event that may bedetected by a probe beam. Subsequently, heat decays into both a sapphirelayer, as well as a silicon on top, as seen, for example, in theembodiment of FIG. 9 . In an embodiment of the invention where there isno film on top of the sapphire, for example, as shown in the embodimentof FIG. 8 , the thermal signature is distinctly different because of thelack of thermal mass transferring some of the heat away from a sapphirelayer.

The pertinent thermophysical properties of, for example, sapphire isknown, namely heat capacity and thermal conductivity, and therefore thesensitivity of an embodiment of the invention to thickness of a siliconlayer on top of the sapphire may be modeled. This example and theexamples below assume that a sapphire substrate is infinite, which isappropriate given the relative dimensions of the sapphire substratecompared to the thin films. In this example, an embodiment of theinvention is extremely sensitive to the thickness of the silicon layereven for a one-nanometer silicon film. This is shown in FIG. 12 , whichdepicts the results of a simulation of an embodiment of the invention'ssensitivity. This simulation and the simulations discussed in theexamples below are based off of numerical solutions to the modulatedheat equation, as detailed elsewhere for FDTR [31]. Since an embodimentof the invention will enable measurement the FDTR response of SOS systemin the infrared, these sensitivity results are indicative of thesensitivity to film thickness. The interpretation of these sensitivityanalyses in this example and the examples below is that the larger thevalue and larger the slope of these results means the embodiment of theinvention is more sensitive to the parameter of interest, for example,film thickness. In these sensitivity analyses shown in the embodiment ofFIG. 12 , a film thickness of 1 nm for the film of interest is chosen soas to demonstrate that the invention is sensitive to film thickness,even in an ultra-thin regime. Therefore, the analysis clearly show thatembodiments of the invention using an infrared FDTR technique may beextremely accurate in measuring the thickness of silicon films with filmthickness down to 1 nm when on sapphire substrates.

Example and Experimental Results Set No. 2: Thin Oxide Less than 50nm/Epi-Silicon/Sapphire

In this embodiment of the invention, an oxide film on top of silicon orsapphire may be used as an absorbing layer. A representation of thisscenario is shown, for example, in FIG. 10 , where the oxide layer ontop of the silicon or sapphire is used as an absorbing layer to create amodulated heating event. Because the properties of both sapphire andsilicon are known from Example and Experimental Results Set No. 1,above, the resulting sensitivity are generated in FIG. 13 .

In order to ensure that the energy is only deposited into the oxidefilm, the wavelength used for a pump beam in this embodiment of theinvention is transparent to sapphire, but not the oxide film. Thisvalidates the assumption that the heating event is homogeneouslyoccurring from the oxide layer and not by absorption in the silicon orthe sapphire. In this regard, this embodiment of the invention relies onthe findings from Example and Experimental Results Set No. 1 toappropriately choose the wavelengths necessary to perform themeasurement. The predictive sensitivity of this embodiment of theinvention to oxide films thickness is shown in FIG. 13 , which againdemonstrates the overwhelming sensitivity of the invention to measuringthe thickness of 1 nm oxide on silicon or sapphire substrates.

Example and Experimental Results Set No. 3: Oxide of Thickness Between40 nm and 1.4 Microns on Sapphire

This embodiment of the invention is similar to Example and ExperimentalResults Set No. 2, as depicted in, for example, FIG. 10 . In thisembodiment of the invention, absorption occurs in an oxide layer, andthis embodiment of invention is therefore sensitive to the thickness ofthe oxide layer on sapphire. Again, drawing from Example andExperimental Results Set No. 1 ensures that this embodiment of theinvention is only absorbing in the oxide layer and not in the underlyingsapphire substrate in order to take the correct assumptions for thesolution to the heat transfer problem.

Example and Experimental Results Set No. 4: Between a Monolayer and 300nm of p-Si or a-Si/Thin Oxide/Sapphire

In this embodiment of the invention, absorption occurs in an underlyingoxide layer, and heat transfer into both a silicon layer above and asapphire layer below affects how heat dissipates in this embodiment ofthe invention. FIG. 14 , for example, shows that this embodiment of theinvention is still sensitive to the thickness of the silicon layer ontop of the oxide and sapphire stack even when absorbing in theunderlying oxide layer. It should be noted that although this embodimentof the invention uses a 50 nm oxide layer to demonstrate thesensitivity, it is valid for all thickness of the oxide layer.

Example and Experimental Results Set No. 5: Between a Monolayer and 200nm of Nitride/Thin Oxide/Epi-Silicon/Sapphire

In this embodiment of the invention, a thin oxide layer may be used asan absorbing layer in order to measure the thickness of a nitride film.Sensitivity for this embodiment of the invention is similar to Exampleand Experimental Results Set No. 4, above, with the p-Si or a-Si on thinoxide on sapphire.

Example and Experimental Results Set No. 6: Between a Monolayer and 1000nm Nitride/Oxide/Sapphire

In this embodiment of the invention, an oxide layer is again used as anabsorber for a pump beam, similar to Example and Experimental ResultsSet No. 5. Sensitivity of this embodiment of the invention is similar tothe oxide on sapphire case.

Additional Examples

Example 1. A method for measuring at least one property of a targetmaterial using thermoreflectance. The method may comprise:

generating a pump light beam at a pump wavelength with a pump device;

generating a modulated pump beam by modulating an amplitude of anintensity of the pump light beam between at least a first modulationfrequency and a second modulation frequency;

directing at least a portion of the modulated pump beam to amanipulation portion of the target material;

generating a probe beam at a probe wavelength with a probe device;

directing at least a portion of the probe beam to a probing portion ofthe target material, wherein at least a part of the portion of the probebeam is reflected off of the target material forming a reflected probebeam,

-   -   wherein the reflected probe beam has a similar modulated        frequency characteristic as the pump beam;

directing at least a portion of the reflected probe beam to a detectiondevice, wherein the detection devices generates a detection signal fromthe reflected probe beam;

analyzing the detection signal with an analyzing device by receiving thedetection signal with the analyzing device, and calculating the propertyof the target material by comparing the modulated frequencycharacteristics of the reflected probe beam to the modulated frequencycharacteristics of the pump beam; and

wherein at least one of the pump wavelength and the probe wavelength isan infrared wavelength.

Example 2. The method of example 1, wherein the property of the targetmaterial is a thickness of the target material.

Example 3. The method of example 1, wherein the pump device comprises apump fiber laser.

Example 4. The method of example 3, wherein the pump fiber lasercomprises a fiber coupled laser or an in-fiber laser.

Example 5. The method of example 3, wherein the pump fiber laser is asingle mode fiber laser or a multimode fiber laser.

Example 6. The method of example 1, wherein the probe device is a probefiber laser.

Example 7. The method of example 6, wherein the probe fiber lasercomprises a fiber coupled laser or an in-fiber laser.

Example 8. The method of example 6, wherein the probe fiber laser is asingle mode fiber laser or a multimode fiber laser.

Example 9. The method of example 1, wherein generating a modulated pumplight beam, directing at least a portion of the modulated pump lightbeam, and directing at least a portion of the probe light beam, furthercomprise utilizing fiber optic devices and not free-space optics.

Example 10. The method of example 9, wherein generating a modulated pumplight beam further comprises directing at least a portion of the pumplight beam to a modulation device using a fiber optic device and notfree-space optics.

Example 11. The method of example 10, wherein the modulation devicecomprises an in-fiber modulation device.

Example 12. The method of example 1, wherein the test material comprisessilicon on sapphire.

Example 13. The method of example 1, wherein the first modulationfrequency and the second modulation frequency are different frequencies.

Example 14. The method of example 13, wherein modulating the pump beamfurther comprises modulating the amplitude of the intensity of the pumpbeam by sweeping between the first modulation frequency and the secondmodulation frequency.

Example 15. The method of example 1, wherein the first modulationfrequency and the second modulation frequency are in the range fromabout 10 Hz to about 100 GHz.

Example 16. The method of example 1, wherein the first modulationfrequency and the second modulation frequency are in the range fromabout 1 GHz to about 100 GHz.

Example 17. The method of example 1, wherein modulating the amplitudethe intensity of the pump beam further comprises modulating theamplitude of the intensity of the pump beam to produce a sinusoidalwave, a square wave, a triangle wave, or a sawtooth wave.

Example 18. The method of example 1, wherein of the pump wavelength isequal to the probe wavelength.

Example 19. The method of example 1, wherein the pump wavelength isdifferent from the probe wavelength.

Example 20. The method of example 1, wherein the pump wavelength is atleast partially absorptive in sapphire.

Example 21. The method of example 1, wherein the pump wavelength iswithin the range of 200 nm to 15000 nm.

Example 22. The method of example 21, wherein the pump wavelength iswithin the range of about 10 μm to about 12 μm.

Example 23. The method of example 21, wherein the pump wavelength iswithin the range of about 720 nm to about 890 nm, or equal to about 980nm.

Example 24. The method of example 1, wherein the probe wavelength is atleast partially reflective in sapphire.

Example 25. The method of example 1, wherein the probe wavelength is aninfrared wavelength.

Example 26. The method of example 25, wherein the probe wavelength iswithin the range of about 10 μm to about 15 μm.

Example 27. The method of example 25, wherein the probe wavelength isabout 1550 nm.

Example 28. The method of example 1, wherein the analyzing devicecomprises a device capable of performing phase-sensitive detection andheterodyne detection.

Example 29. The method of example 1, wherein the analyzing devicecomprises a vector network analyzer.

Example 30. The method of example 1, further comprising generating amodulated pump magnitude signal representing a magnitude of themodulated pump beam between the at least first modulation frequency andthe second modulation frequency, and a modulated pump phase signalrepresenting a phase of the modulated pump beam between the at leastfirst modulation frequency and the second modulation frequency;generating a reflected probe magnitude signal representing a magnitudeof the reflected probe beam, and a reflected probe phase signalrepresenting a phase of the reflected probe beam; wherein

comparing the detection signal at different times of the modulated pumpbeam further comprises comparing the modulated pump magnitude signal andthe modulated pump phase signal to the reflected probe magnitude signaland the reflected probe phase signal.

Example 31. The method of example 1, wherein directing at least theportion of the modulated pump beam to the manipulation portion of thetarget material generates a spot size of the pump beam on themanipulation portion of the target material; wherein the spot size iswithin the range of about 1 μm to about 50 μm.

Example 32. The method of example 1 (as well as subject matter of one ormore of any combination of examples 2-31, in whole or in part), whereinthe probing portion of the target material is within the manipulationportion of the target material.

Example 33. An apparatus for measuring at least one property of a targetmaterial using thermoreflectance. The apparatus may comprise:

a pump device that generates a pump light beam at a pump wavelength;

a first direction apparatus that directs the pump light beam to amodulation device,

-   -   wherein the modulation device generates a modulated pump beam by        modulating an amplitude of an intensity of the pump light beam        between at least a first modulation frequency and a second        modulation frequency;

a second direction apparatus that directs at least a portion of themodulated pump beam to a manipulation portion of the target material;

a probe device that generates a probe beam at a probe wavelength;

a third direction apparatus that directs at least a portion of the probebeam to a probing portion of the target material, wherein at least apart of the portion of the probe beam is reflected off of the targetmaterial forming a reflected probe beam,

-   -   wherein the reflected probe beam has a similar modulated        frequency characteristic as the pump beam;

a detection device that detects at least a portion of the reflectedprobe beam, and produces a detection signal from the reflected probebeam;

an analyzing device receives the detection signal and calculates theproperty of the target material by comparing the modulated frequencycharacteristics of the reflected probe beam to the modulated frequencycharacteristics of the pump beam; and

wherein at least one of the pump wavelength and the probe wavelength isan infrared wavelength.

Example 34. The apparatus of example 33, wherein the property of thetarget material is a thickness of the target material.

Example 35. The apparatus of example 33, wherein the pump devicecomprises a pump fiber laser.

Example 36. The apparatus of example 35, wherein the pump fiber lasercomprises a fiber coupled laser or an in-fiber laser.

Example 37. The apparatus of example 35, wherein the pump fiber laser isa single mode fiber laser or a multimode fiber laser.

Example 38. The apparatus of example 33, wherein the probe device is aprobe fiber laser.

Example 39. The apparatus of example 38, wherein the probe fiber lasercomprises a fiber coupled laser or an in-fiber laser.

Example 40. The apparatus of example 38, wherein the probe fiber laseris a single mode fiber laser or a multimode fiber laser.

Example 41. The apparatus of example 33, wherein the modulation device,the first direction apparatus, the second direction apparatus, and thethird direction apparatus, comprise fiber optic devices and notfree-space optics.

Example 42. The apparatus of example 41, wherein a fourth directionapparatus directs the at least part of a portion of the reflected probebeam to the detection device.

Example 43. The apparatus of example 42, wherein the fourth directionapparatus comprises a fiber optic device and not free-space optics.

Example 44. The apparatus of example 33, wherein the test materialcomprises silicon on sapphire.

Example 45. The apparatus of example 33, wherein the first modulationfrequency and the second modulation frequency are different frequencies.

Example 46. The apparatus of example 45, wherein the modulation devicegenerates the modulated pump beam by modulating the amplitude of theintensity of the pump light beam by sweeping between the firstmodulation frequency and the second modulation frequency.

Example 47. The apparatus of example 33, wherein the first modulationfrequency and the second modulation frequency are in the range fromabout 10 Hz to about 100 GHz.

Example 48. The apparatus of example 33, wherein the first modulationfrequency and the second modulation frequency are in the range fromabout 1 GHz to about 100 GHz.

Example 49. The apparatus of example 33, wherein the modulation devicegenerates the modulated pump beam by modulating the amplitude of theintensity of the pump light beam to produce a sinusoidal wave, a squarewave, a triangle wave, or a sawtooth wave.

Example 50. The apparatus of example 33, wherein of the pump wavelengthis equal to the probe wavelength.

Example 51. The apparatus of example 33, wherein the pump wavelength isdifferent from the probe wavelength.

Example 52. The apparatus of example 33, wherein the pump wavelength isat least partially absorptive in sapphire.

Example 53. The apparatus of example 33, wherein the pump wavelength iswithin the range of about 200 nm to about 15000 nm.

Example 54. The method of example 53, wherein the pump wavelength iswithin the range of about 10 μm to about 12 μm.

Example 55. The apparatus of example 53, wherein the pump wavelength iswithin the range of about 720 nm to about 890 nm, or equal to about 980nm.

Example 56. The apparatus of example 33, wherein the probe wavelength isat least partially reflective in sapphire.

Example 57. The apparatus of example 33, wherein the probe wavelength isan infrared wavelength.

Example 58. The apparatus of example 57, wherein the probe wavelength iswithin the range of about 10 μm to about 15 μm.

Example 59. The apparatus of example 57, wherein the probe wavelength isabout 1550 nm.

Example 60. The apparatus of example 33, wherein the analyzing devicecomprises a device capable of performing phase-sensitive detection andheterodyne detection.

Example 61. The apparatus of example 33, wherein the analyzing devicecomprises a vector network analyzer.

Example 62. The apparatus of example 33, wherein modulating theamplitude of the intensity of the pump light beam further comprisesgenerating a modulated pump magnitude signal representing a magnitude ofthe modulated pump beam between the at least first modulation frequencyand the second modulation frequency, and a modulated pump phase signalrepresenting a phase of the modulated pump beam between the at leastfirst modulation frequency and the second modulation frequency; thedetection signal further comprises a reflected probe magnitude signalrepresenting a magnitude of the reflected probe beam, and a reflectedprobe phase signal representing a phase of the reflected probe beam;wherein

the analyzing device receives the modulated pump magnitude signal, themodulated pump phase signal, the reflected probe magnitude signal, andthe reflected probe phase signal, and wherein

the analyzing device calculates the property of the target material bycomparing the modulated pump magnitude signal and the modulated pumpphase signal to the reflected probe magnitude signal and the reflectedprobe phase signal.

Example 63. The apparatus of example 33, wherein the portion of themodulated pump beam has a spot size on the manipulation portion of thetarget material; wherein the spot size is within the range of about 1 μmto about 50 μm.

Example 64. The apparatus of example 33 (as well as subject matter ofone or more of any combination of examples 34-63, in whole or in part),wherein the probing portion of the target material is within themanipulation portion of the target material.

Example 65. An apparatus for measuring at least one property of a targetmaterial using thermoreflectance. The apparatus may comprise:

a pump device that generates a pump light beam at a pump wavelength;

a first direction apparatus that directs the pump light beam to amodulation device,

-   -   wherein the modulation device generates a modulated pump beam by        modulating an amplitude of the an intensity of the pump light        beam between at least a first modulation frequency and a second        modulation frequency,

a second direction apparatus that directs at least a portion of themodulated pump beam to a manipulation portion of the target material;

a probe device that generates a probe beam at a probe wavelength;

a third direction apparatus that directs at least a portion of the probebeam to a probing portion of the target material, wherein at least apart of the portion of the probe beam is reflected off of the targetmaterial forming a reflected probe beam,

-   -   wherein the reflected probe beam has a similar modulated        frequency characteristic as the pump beam;

a detection device that detects at least a portion of the reflectedprobe beam, and produces a detection signal from the reflected probebeam;

an analyzing device receives the detection signal and calculates theproperty of the target material by comparing the modulated frequencycharacteristics of the reflected probe beam to the modulated frequencycharacteristics of the pump beam; and

wherein the pump device, the modulation device, the first directionapparatus, the second direction apparatus, the probe device, the thirddirection apparatus comprise fiber optic devices.

Example 66. The apparatus of example 65, wherein the property of thetarget material is a thickness of the target material.

Example 67. The apparatus of example 65, wherein the pump devicecomprises a pump fiber laser.

Example 68. The apparatus of example 67, wherein the pump fiber lasercomprises a fiber coupled laser or an in-fiber laser.

Example 69. The apparatus of example 67, wherein the pump fiber laser isa single mode fiber laser or a multimode fiber laser.

Example 70. The apparatus of example 65, wherein the probe device is aprobe fiber laser.

Example 71. The apparatus of example 70, wherein the probe fiber lasercomprises a fiber coupled laser or an in-fiber laser.

Example 72. The apparatus of example 70, wherein the probe fiber laseris a single mode fiber laser or a multimode fiber laser.

Example 73. The apparatus of example 65, wherein the modulation device,the first direction apparatus, the second direction apparatus, and thethird direction apparatus, comprise fiber optic devices and notfree-space optics.

Example 74. The apparatus of example 73, wherein a fourth directionapparatus directs the at least part of a portion of the reflected probebeam to the detection device.

Example 75. The apparatus of example 74, wherein the fourth directionapparatus comprises a fiber optic device and not free-space optics.

Example 76. The apparatus of example 65, wherein the test materialcomprises silicon on sapphire.

Example 77. The apparatus of example 65, wherein the first modulationfrequency and the second modulation frequency are different frequencies.

Example 78. The apparatus of example 77, wherein the modulation devicegenerates the modulated pump beam by modulating the amplitude of theintensity of the pump light beam by sweeping between the firstmodulation frequency and the second modulation frequency.

Example 79. The apparatus of example 65, wherein the first modulationfrequency and the second modulation frequency are in the range fromabout 10 Hz to about 100 GHz.

Example 80. The apparatus of example 65, wherein the first modulationfrequency and the second modulation frequency are in the range fromabout 1 GHz to about 100 GHz.

Example 81. The apparatus of example 65, wherein the modulation devicegenerates the modulated pump beam by modulating the amplitude of theintensity of the pump light beam to produce a sinusoidal wave, a squarewave, a triangle wave, or a sawtooth wave.

Example 82. The apparatus of example 65, wherein at least one of thepump wavelength and the probe wavelength is an infrared wavelength.

Example 83. The apparatus of example 65, wherein of the pump wavelengthis equal to the probe wavelength.

Example 84. The apparatus of example 65, wherein the pump wavelength isdifferent from the probe wavelength.

Example 85. The apparatus of example 65, wherein the pump wavelength isat least partially absorptive in sapphire.

Example 86. The apparatus of example 65, wherein the pump wavelength iswithin the range of about 200 nm to about 15000 nm.

Example 87. The apparatus of example 86, wherein the pump wavelength iswithin the range of about 10 μm to about 12 μm.

Example 88. The apparatus of example 86, wherein the pump wavelength iswithin the range of about 720 nm to about 890 nm, or equal to about 980nm.

Example 89. The apparatus of example 65, wherein the probe wavelength isat least partially reflective in sapphire.

Example 90. The apparatus of example 65, wherein the probe wavelength isan infrared wavelength.

Example 91. The apparatus of example 90, wherein the probe wavelength iswithin the range of about 10 μm to about 15 μm.

Example 92. The method of example 90, wherein the probe wavelength isabout 1550 nm.

Example 93. The apparatus of example 65, wherein the analyzing devicecomprises a device capable of performing phase-sensitive detection andheterodyne detection.

Example 94. The apparatus of example 65, wherein the analyzing devicecomprises a vector network analyzer.

Example 95. The apparatus of example 65, wherein modulating theamplitude of the intensity of the pump light beam further comprisesgenerating a modulated pump magnitude signal representing a magnitude ofthe modulated pump beam between the at least first modulation frequencyand the second modulation frequency, and a modulated pump phase signalrepresenting a phase of the modulated pump beam between the at leastfirst modulation frequency and the second modulation frequency; thedetection signal further comprises a reflected probe magnitude signalrepresenting a magnitude of the reflected probe beam, and a reflectedprobe phase signal representing a phase of the reflected probe beam;wherein

the analyzing device receives the modulated pump magnitude signal, themodulated pump phase signal, the reflected probe magnitude signal, andthe reflected probe phase signal, and wherein

the analyzing device calculates the property of the target material bycomparing the modulated pump magnitude signal and the modulated pumpphase signal to the reflected probe magnitude signal and the reflectedprobe phase signal.

Example 96. The apparatus of example 65, wherein the portion of themodulated pump beam has a spot size on the manipulation portion of thetarget material; wherein the spot size is within the range of about 1 μmto about 50 μm.

Example 97. The apparatus of example 65 (as well as subject matter ofone or more of any combination of examples 66-96, in whole or in part),wherein the probing portion of the target material is within themanipulation portion of the target material.

Example 98. The method of using any of the devices, apparatuses,systems, assemblies, or their components provided in any one or more ofexamples 33-97.

Example 99. The method of providing instructions to use or operate ofany of the devices, apparatuses, systems, assemblies, or theircomponents provided in any one or more of examples 33-97.

Example 100. The method of manufacturing any of the devices,apparatuses, systems, assemblies, or their components provided in anyone or more of examples 33-97.

Example 101. It is noted that machine readable medium or computeruseable medium may be configured to execute the subject matterpertaining to system, devices, apparatuses or related methods disclosedin examples 1-97, as well as examples 98-100.

Example 102. An apparatus including subject matter of one or more of anycombination of examples 33-97, in whole or in part.

PUBLICATIONS

The following patents, applications and publications as listed below andthroughout this document may utilize aspects disclosed in the followingreferences, applications, publications and patents and which are herebyincorporated by reference herein in their entirety (and which are notadmitted to be prior art with respect to the present invention byinclusion in this section):

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Jaskulek, “Monolithic digital galvanic isloation buffer    fabricated in silicon on sapphire CMOS,” Electronics Letters 41,    526-528 (2005).-   7. Z. Fu and E. Culurciello, “An ultra-low power silicon-on-sapphire    ADC for energy scavenging sensors,” IEEE International Symposium on    Circuits and Systems 2006 IEEE ISCS, 1514-1518 (2006).-   8. E. Culurciello, P. O. Pouliquen and A. G. Andreou, “Isolation    charge pump fabricated in silicon on sapphire CMOS technology,”    Electronics Letters 41, 590-592 (2005).-   9. T. Kaya, H. Koser and E. Culurciello, “Low-voltage temperature    sensor for micro-power harvesters in silicon-on-sapphire CMOS,”    Electronics Letters 42, 526-528 (2006).-   10. A. H. Jayatissa, T. Yamaguchi, K. Sawada, M. Aoyama and F. Sato,    “Characterization of interface layer of silicon on sapphire using    spectroscopic ellipsometry,” Japanese Journal of Physics 36,    7152-7155 (1997).-   11. D. Lane, “The optical properties and laser irradiation of some    common glasses,” Journal of Physics D: Applied Physics 23, 1727-1734    (1990).-   12. E. R. Lippincott, A. van Valkenburg, C. E. Weir and E. N.    Bunting, “Infrared studies on polymorphs of silicon dioxide and    germanium dioxide,” Journal of Research of the National Bureau of    Standards 61, 61-70 (1958).-   13. M. A. Hossoin and B. M. Arora, “Optical characterization of    intrinsic poly silicon film for photovoltaic application on sapphire    and TiO₂ substrate by HWCVD,” International Conference on Electrical    Engineering ann Information & Communication Technology 2014 ICEEICT,    1-4 (2014).-   14. H. T. Grahn, H. J. Maris and J. Tauc, “Picosecond ultrasonics,”    Quantum Electronics, IEEE Journal of 25, 2562-2569 (1989).-   15. C. Thomsen, J. Strait, Z. Vardeny, H. J. Maris, J. Tauc    and J. J. Hauser, “Coherent phonon generation and detection by    picosecond light pulses,” Physical Review Letters 53, 989-992    (1984).-   16. C. Thomsen, H. T. Grahn, H. J. Maris and J. Tauc, “Surface    generation and detection of phonons by picosecond light pulses,”    Physical Review B 34, 4129-4138 (1986).-   17. C. S. Gorham, K. Hattar, R. Cheaito, J. C. Duda, J. T.    Gaskins, T. E. Beechem, J. F. Ihlefeld, L. B. Biedermann, E. S.    Piekos, D. L. Medlin and P. E. Hopkins, “Ion irradiation of the    native oxide/silicon surface increases the thermal boundary    conductance across aluminum/silicon interfaces,” Physical Review B    90, 024301 (2014).-   18. G. T. Hohensee, W.-P. Hsieh, M. D. Losego and D. G. Cahill,    “Interpreting picosecond acoustics in the case of low interface    stiffness,” Review of Scientific Instruments 83, 114902 (2012).-   19. D. G. Cahill, P. V. Braun, G. Chen, D. R. Clarke, S. Fan, K. E.    Goodson, P. Keblinski, W. P. King, G. D. Mahan, A. Majumdar, H. J.    Maris, S. R. Phillpot, E. Pop and L. Shi, “Nanoscale thermal    transport. II. 2003-2012,” Applied Physics Reviews 1, 011305 (2014).-   20. D. G. Cahill, K. E. Goodson and A. Majumdar, “Thermometry and    thermal transport in micro/nanoscale solid-state devices and    structures,” Journal of Heat Transfer 124, 223-241 (2002).-   21. R. Rosei and D. W. Lynch, “Thermomodulation spectra of Al, Au,    and Cu,” Physical Review B 5, 3883-3894 (1972).-   22. R. Rosei, “Temperature modulation of the optical transitions    involving the Fermi surface in Ag: Theory,” Physical Review B 10,    474-483 (1974).-   23. R. Rosei, C. H. Culp and J. H. Weaver, “Temperature modulation    of the optical transitions involving the Fermi surface in Ag:    Experimental,” Physical Review B 10, 484-489 (1974).-   24. P. E. Hopkins, “Effects of electron-boundary scattering on    changes in thermoreflectance in thin metal films undergoing    intraband excitations,” Journal of Applied Physics 105, 093517    (2009).-   25. P. E. Hopkins, “Influence of electron-boundary scattering on    thermoreflectance calculations after intra- and interband    transitions induced by short-pulsed laser absorption,” Physical    Review B 81, 035413 (2010).-   26. Y. Wang, J. Y. Park, Y. K. Koh and D. G. Cahill,    “Thermoreflectance of metal transducers for time-domain    thermoreflectance,” Journal of Applied Physics 108, 043507 (2010).-   27. R. B. Wilson, B. A. Apgar, L. W. Martin and D. G. Cahill,    “Thermoreflectance of metal transducers for optical pump-probe    studies of thermal properties,” Optics Express 20, 28829-28838    (2012).-   28. C. A. Paddock and G. L. Eesley, “Transient thermoreflectance    from thin metal films,” Journal of Applied Physics 60, 285-290    (1986).-   29. D. G. Cahill, “Analysis of heat flow in layered structures for    time-domain thermoreflectance,” Review of Scientific Instruments 75,    5119-5122 (2004).-   30. R. M. Costescu, M. A. Wall and D. G. Cahill, “Thermal    conductance of epitaxial interfaces,” Physical Review B 67, 054302    (2003).-   31. A. J. Schmidt, “Pump-probe thermoreflectance,” Annual Review of    Heat

Transfer 16, 159-181 (2013).

-   32. A. J. Schmidt, R. Cheaito and M. Chiesa, “A frequency-domain    thermoreflectance method for the characterization of thermal    properties,” Review of Scientific Instruments 80, 094901 (2009).-   33. J. Yang, E. Ziade, C. Maragliano, R. Crowder, X. Wang, M.    Stefancich, M. Chiesa, A. K. Swan and A. J. Schmidt, “Thermal    conductance imaging of graphene contacts,” Journal of Applied    Physics 116, 023515 (2014).-   34. A. J. Schmidt, R. Cheaito and M. Chiesa, “Characterization of    thin metals films via frequency-domain thermoreflectance,” Journal    of Applied Physics 107, 024908 (2010).-   35. P. E. Hopkins, J. R. Serrano, L. M. Phinney, S. P.    Kearney, T. W. Grasser and C. T. Harris, “Criteria for cross-plane    dominated thermal transport in multilayer thin film systems during    modulated laser heating,” Journal of Heat Transfer 132, 081302    (2010).-   36. J. Yang, E. Ziade and A. J. Schmidt, “Modeling optical    absorption for thermoreflectance measurements,” Journal of Applied    Physics 119, 095107 (2016).-   37. J. T. Gaskins, A. Bulusu, A. J. Giordano, J. C. Duda, S. Graham    and P. E. Hopkins, “Thermal conductance across phosphonic acid    molecules and interfaces: Ballistic versus diffusive vibrational    transport in molecular monolayers,” Journal of Physical Chemistry C    119, 20931-20939 (2015).-   38. C. S. Gorham, J. T. Gaskins, G. N. Parsons, M. D. Losego    and P. E. Hopkins, “Density dependence of the room temperature    thermal conductivity of atomic layer deposition grown amorphous    alumina (Al₂O₃),” Applied Physics Letters 104, 253107 (2014).-   39. P. E. Hopkins, “Vacancy and interface effects on phonon thermal    transport in oxide nanostructures,” Electronic Materials and    Applications (Orlando, Fla., 2016).

REFERENCES

The devices, systems, apparatus, materials, compositions, components,computer readable medium, computer processors, and methods (ofmanufacture and use) of various embodiments of the invention disclosedherein may utilize aspects disclosed in the following references,applications, publications and patents and which are hereby incorporatedby reference herein in their entirety (and which are not admitted to beprior art with respect to the present invention by inclusion in thissection):

-   A. Jonathan A. Malen, Kanhayalal Baheti, Tao Tong, Yang Zhao,    Janice A. Hudgings, Arun Majumdar, “Optical Measurement of Thermal    Conductivity Using Fiber Aligned Frequency Domain Thermoreflectance,    133 Journal of Heat Transfer (Jun. 13, 2011).-   B. Aaron J. Schmidt, Ramez Cheaito, and Matteo Chiesa, A    frequency-domain thermoreflectance method for the characterization    of thermal properties, 80 Review of Scientific Instruments (2009).-   C. Dongliang Zhao, Xin Qian, Xiaokun Gu, Saad Ayub Jajja, Ronggui    Yang, “Measurement Techniques for Thermal Conductivity and    Interfacial Thermal Conductance of Bulk and Thin Film Materials,”    available at https://arxiv.org/abs/1605.08469.-   D. James Christofferson, Ali Shakouri, Thermal measurements of    active semiconductor micro-structures acquired through the substrate    using near IR thermoreflectance, 35 Microelectronics Journal 791-96    (2004).-   E. U.S. Pat. No. 8,264,693 B2, Stoica, et al., “Method and System    for Measuring at Least One Property Including a Magnetic Property of    a Material Using Pulsed Laser Sources”, Sep. 11, 2012.-   F. U.S. Pat. No. 7,619,741 B2, Nicolaides, L., et al., “Modulated    Reflectance Measurement System with Multiple Wavelengths”, Nov. 17,    2009.-   G. R. B. Wilson, Brent A. Apgar, Lane W. Martin, and David G.    Cahill, Thermoreflectance of metal transducers for optical    pump-probe studies of thermal properties, 20 Optics Express (2010).-   H. Fabian D. J. Brunner, Arno Schneider, and Peter Gunter, A    terahertz time-domain spectrometer for simultaneous transmission and    reflection measurements at normal incidence, 17 Optics Express    20684-93 (2009).-   I. Thomas M E, Joseph R I, Tropf W J, Infrared transmission    properties of sapphire, spinel, yttria, and ALON as a function of    temperature and frequency, 27 Applied Optics 239-45 (1988).-   J. B. Vermeersch, J. Christofferson, K. Maize, Time and frequency    domain CCD-based thermoreflectance techniques for high-resolution    transient thermal imaging, 26th Annual IEEE Semiconductor Thermal    Measurement and Management Symposium (SEMI-THERM) (2010).-   K. Ruoho, M., Valset, K., Finstad, T. & Tittonen, I. Measurement of    thin film thermal conductivity using the laser flash method.    Nanotechnology 26, 195706 (2015).-   L. Campbell, R. C., Smith, S. E. & Dietz, R. L. Measurements of    adhesive bondline effective thermal conductivity and thermal    resistance using the laser flash method, in Fifteenth Annual IEEE    Semiconductor Thermal Measurement and Management Symposium, 1999    83-97 (1999).-   M. Wang L, Cheaito R, Braun J L, Giri A, Hopkins P E, Thermal    conductivity measurements of non-metals via combined time- and    frequency-domain thermoreflectance without a metal film transducer,    Rev Sci Instrum (2016).-   N. Jie Zhu, Dawei Tang, Wei Wang, Jun Liu, Kristopher W. Holub,    Ronggui Yang, Ultrafast thermoreflectance techniques for measuring    thermal conductivity and interface thermal conductance of thin    films, 18 Journal of Applied Physics (2010).-   O. C. Thomsen, J. Strait, Z. Vardeny, H. J. Maris, J. Tauc and J. J.    Hauser, “Coherent phonon generation and detection by picosecond    light pulses,” Physical Review Letters 53, 989-992 (1984).-   P. C. Thomsen, H. T. Grahn, H. J. Maris and J. Tauc, “Surface    generation and detection of phonons by picosecond light pulses,”    Physical Review B 34, 4129-4138 (1986).-   Q. Jie Zhu, Dawei Tang, Wei Wang, Jun Liu, Ronggui Yang,    Frequency-Domain Thermoreflectance Technique for Measuring Thermal    Conductivity and Interface Thermal Conductance of Thin Films, 14th    International Heat Transfer Conference, Volume 6 (2010).-   R. Yarai, A., et al., “Laptop photothermal reflectance measurement    instrument assembled with optical fiber components”, Review of    Scientific Instruments 78, 054903-1-5, (2007).

Unless clearly specified to the contrary, there is no requirement forany particular described or illustrated activity or element, anyparticular sequence or such activities, any particular size, speed,material, duration, contour, dimension or frequency, or any particularlyinterrelationship of such elements. Moreover, any activity can berepeated, any activity can be performed by multiple entities, and/or anyelement can be duplicated. Further, any activity or element can beexcluded, the sequence of activities can vary, and/or theinterrelationship of elements can vary. It should be appreciated thataspects of the present invention may have a variety of sizes, contours,shapes, compositions and materials as desired or required.

In summary, while the present invention has been described with respectto specific embodiments, many modifications, variations, alterations,substitutions, and equivalents will be apparent to those skilled in theart. The present invention is not to be limited in scope by the specificembodiment described herein. Indeed, various modifications of thepresent invention, in addition to those described herein, will beapparent to those of skill in the art from the foregoing description andaccompanying drawings. Accordingly, the invention is to be considered aslimited only by the spirit and scope of the following claims, includingall modifications and equivalents.

Still other embodiments will become readily apparent to those skilled inthis art from reading the above-recited detailed description anddrawings of certain exemplary embodiments. It should be understood thatnumerous variations, modifications, and additional embodiments arepossible, and accordingly, all such variations, modifications, andembodiments are to be regarded as being within the spirit and scope ofthis application. For example, regardless of the content of any portion(e.g., title, field, background, summary, abstract, drawing figure,etc.) of this application, unless clearly specified to the contrary,there is no requirement for the inclusion in any claim herein or of anyapplication claiming priority hereto of any particular described orillustrated activity or element, any particular sequence of suchactivities, or any particular interrelationship of such elements.Moreover, any activity can be repeated, any activity can be performed bymultiple entities, and/or any element can be duplicated. Further, anyactivity or element can be excluded, the sequence of activities canvary, and/or the interrelationship of elements can vary. Unless clearlyspecified to the contrary, there is no requirement for any particulardescribed or illustrated activity or element, any particular sequence orsuch activities, any particular size, speed, material, dimension orfrequency, or any particularly interrelationship of such elements.Accordingly, the descriptions and drawings are to be regarded asillustrative in nature, and not as restrictive. Moreover, when anynumber or range is described herein, unless clearly stated otherwise,that number or range is approximate. When any range is described herein,unless clearly stated otherwise, that range includes all values thereinand all sub ranges therein. Any information in any material (e.g., aUnited States/foreign patent, United States/foreign patent application,book, article, etc.) that has been incorporated by reference herein, isonly incorporated by reference to the extent that no conflict existsbetween such information and the other statements and drawings set forthherein. In the event of such conflict, including a conflict that wouldrender invalid any claim herein or seeking priority hereto, then anysuch conflicting information in such incorporated by reference materialis specifically not incorporated by reference herein.

We claim:
 1. A method for measuring at least one property of a targetmaterial using thermoreflectance, the method comprising: generating apump light beam at a pump wavelength with a pump device; generating amodulated pump beam by modulating an amplitude of an intensity of thepump light beam by sweeping between at least a first modulationfrequency and a different second modulation frequency; directing atleast a portion of the modulated pump beam to a manipulation portion ofthe target material; generating a probe beam at a probe wavelength witha probe device; directing at least a portion of the probe beam to aprobing portion of the target material, wherein at least a part of theportion of the probe beam is reflected off of the target materialforming a reflected probe beam, wherein the reflected probe beam has asimilar modulated frequency characteristic as the pump beam; directingat least a portion of the reflected probe beam to a detection device,wherein the detection devices generates a detection signal from thereflected probe beam; and analyzing the detection signal with ananalyzing device by receiving the detection signal with the analyzingdevice, and calculating the property of the target material by comparingthe modulated frequency characteristics of the reflected probe beam tothe modulated frequency characteristics of the pump beam; and wherein atleast one of the pump wavelength and the probe wavelength is an infraredwavelength.
 2. The method of claim 1, wherein the property of the targetmaterial is a thickness of the target material.
 3. The method of claim1, wherein the pump device comprises a pump fiber laser.
 4. The methodof claim 3, wherein the pump fiber laser comprises a fiber coupled laseror an in-fiber laser.
 5. The method of claim 3, wherein the pump fiberlaser is a single mode fiber laser or a multimode fiber laser.
 6. Themethod of claim 1, wherein the probe device is a probe fiber laser. 7.The method of claim 6, wherein the probe fiber laser comprises a fibercoupled laser or an in-fiber laser.
 8. The method of claim 6, whereinthe probe fiber laser is a single mode fiber laser or a multimode fiberlaser.
 9. The method of claim 1, wherein generating a modulated pumplight beam, directing at least a portion of the modulated pump lightbeam, and directing at least a portion of the probe light beam, furthercomprise utilizing fiber optic devices and not free-space optics. 10.The method of claim 9, wherein generating a modulated pump light beamfurther comprises directing at least a portion of the pump light beam toa modulation device using a fiber optic device and not free-spaceoptics.
 11. The method of claim 10, wherein the modulation devicecomprises an in-fiber modulation device.
 12. The method of claim 1,wherein the target material comprises silicon on sapphire.
 13. Themethod of claim 1, wherein the first modulation frequency and the secondmodulation frequency are in a range from about 10 Hz to about 100 GHz.14. The method of claim 1, wherein the first modulation frequency andthe second modulation frequency are in a range from about 1 GHz to about100 GHz.
 15. The method of claim 1, wherein modulating the amplitude theintensity of the pump beam further comprises modulating the amplitude ofthe intensity of the pump beam to produce a sinusoidal wave, a squarewave, a triangle wave, or a sawtooth wave.
 16. The method of claim 1,wherein of the pump wavelength is equal to the probe wavelength.
 17. Themethod of claim 1, wherein the pump wavelength is different from theprobe wavelength.
 18. The method of claim 1, wherein the pump wavelengthis at least partially absorptive in sapphire.